The present invention relates to a novel and useful composite structure which is particularly useful as a firewall.
xe2x80x9cFirewallsxe2x80x9d or xe2x80x9cfireproof wallsxe2x80x9d are widely employed in buildings and vehicles to separate potential sources of ignition from flammable liquids and vapors. Firewalls are particularly useful in vehicles such as aircraft and aerospace modules. With respect to aircraft, the United States Federal Aeronautics Administration requires xe2x80x9cfire proofxe2x80x9d barriers or walls between ignition sources and flammable liquids and/or vapors. The status of xe2x80x9cfireproofxe2x80x9d is defined as the capability of a material or component to withstand a 2,000xc2x0 F. flame for 15 minutes without any flames being observed on the backside of the wall or barrier due to flame penetration. Examples of areas in aircraft that require firewalls are the engine power section, auxiliary power units, fuel-burning heaters, engines accessory sensors, and the like. Such areas are designated as xe2x80x9cfire zonesxe2x80x9d.
In the past, firewalls have been formed of stiffened metallic sheets, 15 to 20 mils in thickness. Stainless steel, titanium, and corrosion resistant steel have been used in this regard. Such metallic entities are heavy and are very poor insulators. In addition, spray-on coatings and blankets have also been used to clad surfaces, for providing insulation and protection. Such spray-on and blanket insulation systems are expensive, heavy, and are difficult to maintain and install.
Carbon based honeycombs have been recognized as exhibiting normal heat conductivity along a controlled direction. For example, U.S. Pat. Nos. 5,470,633 and 5,527,584 describe such honeycomb structures.
Other fire resistant materials have been proposed such as those found in U.S. Pat. No. 6,013,361, which describes a high performance laminate composite material utilizing a resin impregnating fiber. Such fiber may take the form of graphite.
U.S. Pat. Nos. 4,595,714 and 4,656,095 describe ablative of coating compositions utilizing a mixture of epoxy, polysulfide resins, an amine curing agent, refractory fibers, and inorganic materials to form a glassy reaction product when exposed to heat, which provides thermal protection.
U.S. Pat. Nos. 5,015,522 and 5,024,877 show fire resistant carbonatous material mixed with polymeric material such as organosilicone polymer to increase fire resistance.
U.S. Pat. No. 4,255,483 describes fire barrier compositions and composites utilizing silica-containing material and a resin which is applied to a graphite fiber or cloth to form a composite structure which is flame resistant.
U.S. Pat. No. 5,558,932 describes a structural composite flame barrier which employs a structural polymer composite and a ceramic matrix which are adhered to one another to form an integrated structural panel.
U.S. Pat. No. 4,522,673 teaches a heat-insulating blanket where heat and fire resistant fabrics are placed on either side of a layer of insulating material to protect the same in high heat environments.
U.S. Pat. No. 4,767,656 describes a composite material possessing fire protection capability which utilizes polyimide resins in a woven ceramic fabric that surrounds the resin. The layers may be formed into a honeycomb.
U.S. Pat. No. 4,567,076 reveals a load bearing composite structure possessing thermal and flame resistance in which a honeycomb structure is sandwiched between plies, one of which is sewn together to a blanket and cured. The honeycomb is generally a glass fiber reinforced polyimide core while the blanket is generally formed of ceramic fabric.
U.S. Pat. No. 4,659,624 shows a carbon-carbon laminate which may be coded with fire resistant materials to provide protection in high temperature conditions for resistance to degradation by oxidation.
Carbon-carbon materials have been known for many years which retain strength and stiffness at high temperatures in an inert atmosphere. Carbon-carbon materials are generally resistant to thermal shock and creep. However, carbon-carbon materials have generally been excluded from oxidation environments at high temperatures, usually greater than 400xc2x0 C.
A fireproof structure which is useful as a firewall and is light and strong would be an extraordinary advance in the field of structural materials.
In accordance with the present invention a novel and useful fireproof composite structure, useable as a firewall, is herein provided.
The structure of the present invention utilizes a sheet of carbon-carbon material which is formed with a first side and an opposite second side. The sheet of material is of sufficient size and stiffness to provide structural integrity when used as a firewall. The first side of the sheet of material is subject to flame impingement, such that a flame possessing a temperature of about 2,000xc2x0 F. on the first side will not penetrate the sheet and be observable on the second side over a 15-minute period. The sheet of carbon-carbon material may initially comprise a pan, pitch, rayon, or other carbon forming material which is densified, following pyrolysis, preferably by chemical vapor infiltration (CVI). The CVI process introduces a hydrocarbon gas into a chamber where the pyrolytic carbon is placed. At about 2,000xc2x0 F., and at a pressure ranging from 500 to 3,000 Pa, densification takes place resulting in a sheet of carbon-carbon material which may possess a density in the range of 1-2 grams/cm3.
In another embodiment of the present invention, multiple sheets such as first and second sheets or plies of carbon-carbon material are formed in the same manner with respect to the single sheet of carbon-carbon material. However the sheets are held or bonded to one another such that one side of one sheet of carbon-carbon material is exposed to the flame while the backside of another sheet of carbon-carbon material lies adjacent the flammable gas or liquid being protected by the firewall. Again, the first and second sheets of carbon-carbon material would exhibit sufficient structural integrity to serve as a firewall. Bonding between the sheets may take place by the use of an epoxy resin or other similar known adhesive compounds.
Yet another embodiment of the present invention utilizes first and second sheets of carbon-carbon material formed according to the hereinabove described process. However, a honeycomb of carbon-carbon material would lie between, and be bonded to, the first and second sheets to form a unit. One side of the first sheet of the unit would be subject to flame impingement while another side of the second sheet of the unit sandwiching the honeycomb core would lie adjacent the flammable materials being protected by the firewall.
In any case, the structures of the present invention would be subject to a flame at 2,000xc2x0 F. which is incapable of penetrating the sheet, laminate, or unit over a 15 minute period, such that the flame is not observable on the backside of any of the structures of the present invention hereinabove described.
It may be apparent that a novel and useful fire proof composite structure, useable as a firewall has been hereinabove described.
It is therefore an object of the present invention to provide a fireproof composite structure useable as a firewall which provides thermal and flame protection and is rated as fire proof according to standard tests.
Another object of the present invention is to provide a fireproof composite structure useable as a firewall which is of a very low density and possesses very high stiffness.
A further object of the present invention is to provide a fireproof composite structure which is useable as a firewall that may be substituted for presently constructed firewalls in aircraft and aerospace vehicles.
Yet another object of the present invention is to provide a fireproof composite structure which is useable as a firewall that eliminates the need for auxiliary insulation and allows heat sensitive materials, such as wiring, to lie very close to the backside of the firewall opposite impingement of a flame.
Another object of the present invention is to provide a fireproof composite structure which is useable as a firewall and eliminates the need for reinforcing or stiffening structures, thus, reducing the cost and complexity of the structure.
The invention possesses other objects and advantages especially as concerns particular characteristics and features thereof which will become apparent as the specification continues.